a. Field of the Invention
The present invention relates to spacer frame bars which are used to maintain separation between glass panes in insulated glass windows and other panels and, in particular, to a spacer frame bar having an upper web which is configured to create a lengthened thermal path between the glass panes without causing a significant increase in thermal gain when exposed to solar radiation.
b. Related Art
It is well known in the art to provide a window with more than one pane of glass separated by an airspace. Such windows are known as insulating windows or insulated glass panels, by virtue of the fact that the air and/or other gasses (argon, helium, nitrogen, etc.) trapped within the space between the glass panes serves as an insulator to reduce heat flow through the window.
Typically, the glass panes are separated by a spacer frame which lies between the glass panes and extends around their perimeter. The spacer frame is typically constructed of sections of tubular material, also known as spacer frame bars, which are usually made of a metal such as aluminum alloy, steel or stainless steel. In addition to being commercially economical, these materials have the strength and rigidity which are required in order for the spacer frame serve its structural functions. Also, aluminum and steel exhibit good corrosion resistance and are stable over a wide range of temperatures, and the structural integrity of these materials is not adversely affected by long-term exposure to sunlight.
The use of aluminum, steel or other metals in a spacer frame, however, is not without its problems. A significant heat transfer problem may arise because an aluminum or metal spacer is a much better heat conductor than the surrounding airspace. Because the spacer and glass panes are contiguous, the spacer itself acts as a conduit for energy transfer between inside and outside panes of glass. Thus, significant energy loss may result because of the spacer""s physical contact with the glass panes.
Moreover, heat transfer through the spacer may cause the edge or other area of the window which is in contact with the spacer to be at a significantly higher or lower temperature than the rest of the pane. In particular, where outside temperatures are cold, this may cause the edges of the window to be relatively cool around the interior pane (i.e., cooler than the interior of the building), resulting in serious condensation problems.
One partial solution to heat transfer through the spacer is provided by U.S. Pat. No. 5,568,714 to Peterson. The invention of Peterson provides an elongate tubular spacer with an integral thermal break that reduces energy flow between glass panes. Although the thermal break impedes heat transfer through the spacer, heat transfer impedance can still be an issue because the metal on either side of the thermal break still rapidly conducts thermal energy.
Another partial solution is provided by U.S. Pat. No. 5,377,473 to Narayan et al. The invention of Narayan provides a spacer having a lower web which is generally W-shaped in cross-section, and an upper web which is pierced by a series of slots which are intended to eliminate straight-line thermal paths across the web and also to allow fluid contact between the air in the interpane space and a desiccant material inside the spacer. Unfortunately, the slots also allow the desiccant material (typically, a silica gel or other material which is in granular form so as to maximize surface area) to escape from the spacer and into the interpane space, where it tends to foul the inside surfaces of the panes.
Although some prior attempts have thus been made to reduce heat transfer through a spacer by forming a lengthened thermal path in one way or another, the results have been somewhat mixed. In particular, the upper web of the spacer (i.e., that part of the spacer which faces inwardly towards the interpane space) has remained something of a xe2x80x9cweak link,xe2x80x9d in that this often forms the shortest, most direct thermal path between the two panes. Typically, the upper web has been confined to a generally horizontal plane, extending perpendicular to the planes of the glass, both for aesthetic reasons and also because the upper web of the spacer must not project above the xe2x80x9csight linexe2x80x9d of the window or else it will obstruct and reduce the available viewing area.
An additional complication relates to the fact that the upper web of the spacer is typically exposed to fairly intense solar radiation, i.e., sunlight. Absorption of solar radiation causes thermal gain (i.e., heating) in the spacer unit, with the thermal energy being transferred to the adjoining panes. This can be a serious source of thermal inefficiency, particularly in hot, sunny climates. For example, in such climates the interiors of buildings are commonly air-conditioned, and in a large building (such as a commercial office tower) the combined thermal gain of the spacers in the numerous windows can contribute significantly to the load on the air-conditioning plant. Therefore, it is generally desirable to reduce the tendency of the spacer to absorb solar radiation, and, conversely, any configurations which are intended to increase the length of the thermal path across the upper web should not do so at the cost of added absorption of such radiation.
Accordingly, there exists a need for an improved metal spacer bar which defines elongate thermal conductive paths between glass panes, particularly across the top web of the spacer, so as to enhance the thermal efficiency of insulated windows or other panels. Furthermore, there exists a need for such an improved spacer bar which provides such lengthened conductive paths without causing increased thermal gain of the spacer due to absorption of solar radiation. Still further, there exists a there exists a need for such a spacer bar which establishes fluid contact between the air or other gasses in the interpane space and a desiccant material within the bar, but without possibility of the desiccant escaping therefrom into the space between the panes.
The present invention has solved the problems which have been cited above. Broadly, this is a spacer frame bar comprising an elongate tubular spacer member having first and second side webs for engaging first and second glass panes in spaced relationship, and upper and lower webs spanning from the first side web to the second side web and defining a spacer width between the side webs, the upper web of the spacer member comprising at least first and second corrugations formed in the upper web, each corrugation defining an upwardly extending ridge portion and a downwardly extending channel portion so that the corrugations form an elongate thermal energy conductive path across the upper web which is greater in length than the spacer width between the side webs, the corrugations further being oriented so that only an upper edge of each ridge portion is exposed to solar radiation between the glass panes and the channel portions of the corrugations are substantially shaded by adjacent corrugations, so that the upper web of the spacer member forms the elongate conductive path without causing increased thermal gain of the spacer member when the window assembly is exposed to solar radiation.
In a preferred embodiment, the corrugations may comprise a plurality of parallel, longitudinally extending corrugations arranged across the width of the upper web, and the ridge and channel portions of the corrugations may be oriented in a substantially vertical direction.
The upper web of the spacer member may further comprise at least one spaced sequence of longitudinally oriented slits formed through the web in each of the corrugations, so that the slits form a series of thermal breaks across the web. The spaced sequence of slits in each corrugation may be staggered longitudinally relative to the slits in adjacent corrugations.
The spaced sequences of slits may be formed in side walls of the corrugations intermediate the upper ends of the ridge portions and the lower ends of the channel portions. Each corrugation may comprise at least two spaced sequences of slits on opposite sides of the corrugation. The slits may each comprise a first longitudinal edge portion which is displaced relative to a second edge portion by an amount which is sufficient to open an air gap between the edges of the slit.
The spacer member may further comprise at least one insulating member which is mounted in the corrugations of the upper web. The insulating member may comprise a plurality of strips formed of insulating material, each insulating strip being mounted in the channel portion of one of the corrugations. The insulating strips may substantially fill the channel portions so that only an upper crown of each ridge portion is exposed above the insulating material. The insulating material may comprise a resilient foam material.
Each of the channel portions may comprise means for engaging and retaining the strip of insulating material therein. The means for retaining the strip may comprise an inwardly-bent tab portion of a slit formed in the wall of the channel portion, or may comprise at least one inwardly-protruding point formed in the wall of the channel portion.
The spacer member may be formed of inner and outer halves, the halves being joined along upper and lower longitudinally extending seams. The spacer member may also be formed as a two-piece structure in which there is a lower, generally xe2x80x9cUxe2x80x9d shaped channel member which incorporates the lower and side webs of the spacer member, and an upper cap member which incorporates the upper web of the spacer member, the outer edges of the cap member cooperating with the upper edges of the channel member to form connection joints by which the cap member is mounted to the channel member.
The connection joints may each comprise a generally xe2x80x9cVxe2x80x9d shaped receiving channel formed along an upper edge of the channel member, and a flange portion formed along an outer edge of the cap member which extends downwardly therefrom into locking engagement with the channel. The receiving channel may comprise a lip portion which extends downwardly from an edge of the receiving channel to a position above a lower edge of the flange portion, so as to retain the flange portion against being withdrawn upwardly out of the receiving channel. The flange portion, in turn, may comprise a lip portion which extends upwardly from the lower edge thereof so as to engage the lip portion of the receiving channel in substantially vertical abutment therewith.